New York -LRB- CNN -RRB- -- Officer Rafael Ramos sat in the driver 's seat . Officer Wenjian Liu was at his side .

The two cops were n't at their usual precinct -- normally , the pair was assigned to downtown Brooklyn , but they were working a `` critical response '' detail in an area with higher crime , police said .

That 's where they were slain , ambush-style -- Saturday afternoon as they sat in their patrol car , New York Police Commissioner William Bratton said at an evening news conference .

The gunman approached the passenger side of the patrol car and took a shooting stance , witnesses told police . He opened fire several times , striking both officers in the head , Bratton said .

They were `` shot and killed with no warning , no provocation , '' Bratton told reporters . `` They were quite simply , assassinated . ''

The gunman was found dead in a nearby subway station from a self-inflicted gunshot wound .

The thin blue line

The families of the fallen officers rushed to Woodhull Medical Center on Saturday , as dozens of their comrades gathered in a show of support .

Ramos had just turned 40 this month ; Liu got married two months ago .

Both dreamed of being police officers , Bratton said .

`` One of the unfortunate realities of policing is that you put that blue uniform on and you become part of the thin blue line between us and anarchy , '' Bratton said .

Mayor Bill de Blasio and Bratton met with the families of the victims . De Blasio said that Ramos ' 13-year-old son could n't comprehend what had happened to his father .

`` When a police officer is murdered , it tears at the foundation of our society , '' the mayor said . `` It is an attack on the very concept of decency . ''

The suspect

Police identified the shooter as Ismaaiyl Brinsley .

He arrived in New York from Baltimore , but had a residence in Atlanta . Bratton said that Brinsley was somehow connected to Brooklyn , but would not discuss that information .

Bratton said at this time , there was no indication Brinsley was connected to any terrorist groups or organized entity .

Police were investigating posts Brinsley allegedly made on social media . Bratton said that the suspect had earlier shot and seriously wounded a woman believed to be his ex-girlfriend in Baltimore .

Baltimore police received information that Brinsley had made threatening comments about police , and sent a warning to police in New York , Bratton said .

That message came almost the same time the ambush happened .

U.S. Attorney General Eric Holder called the attack `` an unspeakable act of barbarism . ''

De Blasio also called the shootings an `` assassination . ''

`` It is an attack on all of us , '' he said . `` It is an attack on everything we hold dear . ''

A White House official says President Barack Obama was briefed on the shooting .

`` This ca n't happen ''

The shooting jolted residents in the neighborhood .

`` This ca n't happen . If you mad at somebody , be mad at the person that you are mad at . Now , we have two families that -LRB- are -RRB- missing somebody for the holidays , '' Shaniqua Pervis told CNN affiliate WABC .

`` Where is your humanity ? I know it 's a war going on and shoutout to Eric Garner 's family and everybody else who lost somebody , but you 're not at his house , on his lawn . This is two -LRB- officers -RRB- . You do n't even know if -LRB- they were -RRB- good or bad . I do n't condone this , and I 'm not with it . ''

The woman was referring to the controversial July death of the unarmed black man after New York police officers on Staten Island wrestled him to the ground , with one of the officers wrapping his arm around Garner 's neck in a chokehold .

A grand jury 's decision not to indict the police officer in the Garner case , as well as a separate grand jury 's refusal to indict an officer in a controversial police shooting of unarmed teen Michael Brown in Ferguson , Missouri , led to nationwide protests against the police .

Brown 's family condemned Saturday 's slayings .

`` We reject any kind of violence directed toward members of law enforcement . It can not be tolerated . We must work together to bring peace to our communities , '' they said in a statement .

`` Our thoughts and prayers go out to the officers ' families during this incredibly difficult time . ''

In a statement , activist the Rev. Al Sharpton said the Garner family was outraged by news of the shootings .

`` Any use of the names of Eric Garner and Michael Brown , in connection with any violence or killing of police , is reprehensible and against the pursuit of justice in both cases , '' the statement said . `` We have stressed at every rally and march that anyone engaged in any violence is an enemy to the pursuit of justice for Eric Garner and Michael Brown . ''

Tensions between the community and police have heightened around the country since the deaths of Brown and Garner .

`` This could not have come at a worse time , '' City Councilman Robert Cornegy told CNN affiliate PIX .

So far , police have not commented on the motive for the Brooklyn shootings , except to say the officers were not engaging the shooter in any way when they were shot .

CNN 's David Shortell , Mariano Castillo and Kevin Liptak contributed to this report .

@highlight

Baltimore police reached out to NYPD

@highlight

Two NYPD officers , Wenjian Liu and Rafael Ramos , shot in Brooklyn

@highlight

Police have named Ismaaiyl Brinsley as shooter

@highlight

Both officers shot ambush-style while sitting in a patrol car